Sunscreen application is the main strategy used to prevent the maladies inflicted by ultraviolet (UV) radiation. Despite the continuously increasing frequency of sunscreen use worldwide, the prevalence of certain sun exposure-related pathologies, mainly malignant melanoma (a cancer type which is mainly caused by sun exposure), is also on the rise.
The Sun continuously emits two kinds of radiation: electromagnetic and corpuscular. Electromagnetic radiation provides light and warmth, but also consists of invisible radiation which include; visible light, Ultraviolet rays and infrared rays. and ultraviolet give you a tan and a skin burn if you don’t use sunscreen.
One type − ultraviolet (UV) radiation − is composed of three wavelengths:
UVA rays, which range at 320–400 nm and are not absorbed by the ozone layer,
UVB rays, which range 290–320 nm and are partially absorbed by the ozone layer, and
UVC rays, which are stopped by the ozone layer.
The detrimental effects of exposure to UVA and UVB rays, which can cross the epidermis, have been reviewed and it was concluded that such exposure leads to the generation of free radicals, such as reactive oxygen species (ROS), that can cause; DNA/protein/lipid damage, activation of various signaling process, compromised skin defense systems, altered growth, differentiation, senescence and tissue degradation.
Types of Sunscreen UV Filters
Two kinds of UV filters are currently being used in sunscreens for minimization of these adverse effects:
- Chemical (Organic) Filters: octyl methoxycinnamate (OMC), benzophenone-3 (BP-3) or octocrylene, which absorb light in the UV range.
- Physical (Inorganic) Filters: e.g zinc oxide (ZnO) and titanium dioxide (TiO2), which scatter and reflect UV rays.
Sunscreens are usually comprised of more than one of these UV filters, either organic, inorganic or a mixture of both types, which gives broad-spectrum of protection.
Detrimental Effects
Effects are dosage or concentration of exposure based. Many factors might influence human exposure to UV filters: geographic location, season, lifestyle, gender or occupation, which means it can be highly individualized. The main route of exposure is the skin (Dermal), but common human behavior related to sunscreen application, e.g. eating and drinking with sunscreen applied on hands and lips, gastrointestinal or pulmonary exposure can also be considered. From calculations, the total amount of compound absorbed from a single application might be up to 200 mg, or 2.56 mg/kg body weight (bw), assuming an average bw of 78 kg for adult males. Sunscreen filters have been found to peak in the plasma and most importantly breast milk. This report raises concerns about potential prenatal exposure and developmental toxicity of UV filters.\
Available data imply, that sunscreen compounds (Most especially the chemical UV filters) are easily absorbed by the skin, reaches systemic circulation and accumulate in various tissues. They might block vitamin D synthesis or act as endocrine disruptor and lead to developmental toxicity. The endocrine disruptive and developmental toxicity of many organic UV filters in experimental models is well established, these filters seem to be associated with altered estrogen, androgen and progesterone activity, reproductive and developmental toxicity and impaired functioning of the thyroid, liver or kidneys. Since many of UV filters were shown to cross the blood-brain barrier (BBB) due to their lipophilicity, hence, the risk for neurotoxicity also occurs.
Although some UV-related pathologies could be prevented by applying sunscreen, the efficiency and safety of these products is questionable. Long term use of these filters could pose neurotoxic effects. Although more research are still on going on this question.
Ref: J.A. Ruszkiewicz et al. (2017) Toxicology reports Toxicology Reports:245–259